Alkylated aromatic diisocyanates have been known for a substantial period of time and find use in the preparation of polyurethane and polyurea elastomers. The isocyanates are reacted with polyols to produce a polyurethane system which then can be crosslinked with an aromatic diamine to form a polyurethane/urea elastomer or crosslinked with a short chained diol or triol to produce polyurethane elastomers. Alkylated and substituted aromatic isocyanates which have found use in preparing various elastomer systems are noted in the following patents:
British Pat. No. 1,080,739 discloses alkylated mononuclear monoisocyanates and alkylated diphenyl diisocyanates. The isocyanates are characterized as containing a tertiary alkyl group in ortho positions to each isocyanate group to inhibit the reactivity of the isocyanate group. The reduced reactivity permits greater flexibility in carrying out reactions and the utilization of wider variety of reactants for producing elastomer systems. Examples of diphenyl methane diisocyanates having hindered groups include 4,4'-methylene bis(2-tert-butyl aniline) and in 4,4'-methylene bis(2-methyl-6-tert-butylaniline).
U.S. Pat. No. 3,105,845 discloses the preparation of tetraalkylated mononuclear aromatic polyisocyanates and their use in producing a variety of elastomeric systems. One of the advantages of the alkylated mononuclear aromatic isocyanates is in their reduced reactivity and thus provides a more stable "pot life" for polymer intermediates. Examples of diisocyanates include 1,3,5-trimethyl-2,4-diisocyanatobenzene; durene isocyanate and 1,3-dimethyl-2,5-diethyl-4,6-diisocyanatobenzene.
U.S. Pat. No. 4,399,073 discloses a process for producing teritary alkyl isocyanates such as tetramethylxylene diisocyanate, 1,3,5-tris(1-isocyanato-1-methylethyl)benzene and .alpha.,.alpha.-dimethyl-4-isopropenylbenzeneisocyanate.
U.S. Pat. No. 3,878,235 discloses the production of chlorine-containing methylene-bridged diaryl diisocyanates and the use of these diisocyanates for the preparation of polyurethane elastomer systems. The chloro containing methylene bridged diphenyl diisocyanates have low viscosity and low volatility as compared to toluenediisocyanate for example thus reducing the toxicity problem associated with a mononuclear aromatic diisocyanate such as toluenediisocyanate. The ortho-chloro benzyl-toluenediisocyanate was shown to be a stable liquid under extended period of time as whereas the para-chlorobenzyl-toluenediisocyanate was not a stable liquid but exhibited partial solidification on standing.